Ac-dc Difference Research Articles

Improved Stability of Thin‐Film Multijunction Thermal Converters

SUMMARYWe have demonstrated the long‐term stability and environmental durability of a high‐performance thin‐film multijunction thermal converter (TMJTC) with an improved thin‐film thermopile design. We fabricated a new TMJTC with an improved deposition pattern for a Bi‐Sb‐Cu‐based thin‐film thermopile in order to avoid interface delamination between the Bi and the Cu layers. Our TMJTC exhibited good frequency properties, with an ac–dc difference of less than 5 μV/V in the range from 10 Hz to 100 kHz, at a root‐mean‐square (rms) voltage of 10 V. The long‐term stability of the TMJTC has been significantly increased owing to the performance of the developed thin‐film thermopile, as compared with that of previously fabricated TMJTCs, exhibiting an ac–dc difference of less than 2 μV/V after 18 months at room temperature. We also evaluated the temperature, relative humidity, and pressure characteristics of the TMJTC in accordance with the International Electrotechnical Commission (IEC) standards for electronic devices. The measurement results showed that the dependence of the ac–dc transfer difference on the temperature, humidity, and pressure was less than 1 μV/V, which is comparable to the results of thermal converters, constituting the primary standard.

New Technologies to Improve AC-DC Difference Measurements at NIST

New Technologies to Improve AC-DC Difference Measurements at NIST

Automated Multi-Meter Method for the Scaling of Low AC Voltage from 200 mV to 2 mV

A set of seven single junction thermal converter Micropotentiometers (μPots) has been constructed at the National Institute for Standards (NIS), Egypt. This set has been built to cover the low ac voltage ranges from 2 mV to 200 mV at frequencies from 40 Hz up to 20 kHz. The construction of the μPots set has been presented and an adopted calibration method has been performed as well. This method has been performed by means of a step-down procedure using a Digital Multi-Meter (DMM). The scaling procedures have been carried out in sequential steps starting from the calibration of the 200 mV-μpot by using DMM that is accurately calibrated at its 200 mV ac voltage range down to 2 mV-μPot. Furthermore, a new automatic calibration system has been established to achieve the scaling procedures. This system has been specially designed using Laboratory Virtual Instrument Engineering Workbench (LabVIEW) software to overcome the deficiencies of manual methods. The automatic calibration has been investigated of all mPots at different frequencies. The ac-dc differences for the μPots and their uncertainty evaluation from 2 mV to 200 mV at different frequencies from 40 Hz to 20 kHz have been determined.

Improved Measurement of AC–DC Transfer Difference Using a Low-Drift Single-Junction Thermal Converter

We reduced the exponentially decreasing thermal drift of a single-junction thermal converter and performed comparison measurements of the ac-dc transfer difference. The thermal converter was mounted on a metal block using a high-thermal-conductance paste; this treatment is crucial to improving the thermal drift. Numerical calculations using a thermal model that includes the temperature increase on the cold side of the thermocouple can explain the measured thermal drift. Our system, which uses a low-drift thermal converter, allows comparison measurements of the ac-dc transfer difference at a few parts in 107 with a short measurement time if a sufficiently long waiting time is used.

Precision AC–DC Transfer Measurements With a Josephson Waveform Synthesizer and a Buffer Amplifier

Measurements of the ac-dc difference of a thermal converter have been performed using a Josephson waveform synthesizer and a precision buffer amplifier at frequencies from 10 Hz to 4 kHz, showing agreement with conventional standards of better than 1 μV/V up to 1 kHz. In addition, a method of finding the operating parameters of the programmable Josephson array that corresponds to minimal uncertainty is discussed.

Precision AC–DC Difference Measurement System Based on a Programmable Josephson Voltage Standard

A system designed for precision measurement of ac-dc difference of thermal voltage converters in terms of a programmable Josephson voltage standard is under development at the National Measurement Institute, Australia, in collaboration with the National Institute of Advanced Industrial Science and Technology, Japan. The agreement between the new system and calculable thermal converters is presently better than 0.5 μV/V at frequencies up to 40 Hz and voltages up to 0.75 V.

Thermal-Transfer Standard Validation of the Josephson-Voltage-Standard-Locked Sine-Wave Synthesizer

This paper describes a Josephson-voltage-standard-locked synthesizer where a calibrator is used as a sine-wave generator, output whose is controlled by the calculable fundamental of the stepwise sinusoidal wave generated by a programmable Josephson junction array. Such a system combines the versatility of a calibrator with the stability and the accuracy of the Josephson voltage standard. The validity of this method was confirmed with the ac-dc difference measurements of a calibrated thermal-transfer standard. The synthesizer uncertainty inferred is below 1.2 μV/V for waveform frequencies up to 1 kHz and root-mean-square amplitudes ranging from 100 mV to 1 V.

Development of a thermal voltage converter with calculable high‐frequency characteristics

AbstractA thermal‐voltage converter for high‐frequency (HF‐TVC) AC–DC transfer standard has been developed. The HF‐TVC was designed such that the frequency characteristic is calculable from the shape and dimension of the input circuit. A new multi‐junction thermal converter element (JSTC04) has been developed, which has a simple and straight heater configuration to minimize the parasitic impedances in the input circuit. The AC–DC difference of the HF‐TVC was evaluated by two independent methods, with agreement better than 7 µV/V up to 1 MHz. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Final report on APMP.EM-K6.a: APMP international comparison of ac–dc transfer standards at the lowest attainable level of uncertainty

The APMP international comparison of ac–dc transfer standards at the lowest attainable level of uncertainty, APMP.EM-K6a, started in 2000 and concluded in 2003. This comparison has offered the same range and frequencies as the key comparison CCEM-K6a with the view of providing the National Metrology Institutes (NMIs) of the APMP member economies with an opportunity to link the values of their standards for ac–dc transfer difference to the international reference values. The ac–dc difference of the travelling standard was measured with 3 V applied at standard frequencies of 1 kHz, 20 kHz, 100 kHz and 1 MHz, and optional frequencies of 50 kHz and 500 kHz.The travelling standard has not been damaged and has shown excellent stability. The results submitted by the overwhelming majority of the participants lie well within the reported uncertainty. At the standard frequencies the results have been linked to those of the CCEM-K6a key comparison.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

A New Method for Measuring the Level Dependence of AC Shunts

We report on a new method for the measurement of the level dependence of the AC-DC difference of current shunts. The method is based on the use of a binary inductive current divider. A method to compare two AC shunts at common ground is described. Measurement results on two 1-A AC shunts, which consist of different numbers of resistors, indicate that the level dependence between 0.5 and 1 A is less than 2 ?A/A with an uncertainty of less than 7 ?A/A from 1 to 100 kHz.

An Improved Design of a Fully Automated Multiple Output Micropotentiometer

This paper describes in details a new design of a fully automated multiple output micropotentiometer (?pot). A prototype has been built at the National Institute for Standards (NIS), Egypt to establish this highly improved AC voltage source in the millivolt range. The new device offers three different outputs covering a wide frequency range from only one outlet. This valuably supports the precise sourcing ranges of low AC voltage at NIS. The design and the operation theory of this prototype have been discussed in details. An automatic calibration technique has been introduced through specially designed software using the LabVIEW program to enhance the calibration technique and to reduce the uncertainty contributions. Relative small AC-DC differences of our prototype in the three output ranges are fairly verified. The expanded uncertainties of the calibration results for the three output ranges have been faithfully estimated. However, further work is needed to achieve the optimum performance of this new device.

Single-Junction Thermal Voltage Converters With Reduced Uncertainties at Frequencies up to 1 MHz

This paper presents a new realization of standards for ac-dc difference at voltages ranging from 1 to 4 V and frequencies of up to 1 MHz. This work has mainly been focused on improving the determination of the components of ac-dc difference that most significantly contributed to the uncertainty of the previous realization. These components are the ac-dc difference due to skin effect, transmission line effect, and the interaction between parasitic inductances and capacitances, which is described here as the L/C effect. As a result, combined 1 - sigma uncertainties as low as 4.3 muV/V at 1 MHz have been achieved.

Improved High-Input-Impedance mV-Amplifiers With Gain Factors From 10 to 900

New millivolt-amplifiers (mV-amplifiers) driving planar multijunction thermal converters (PMJTCs) at their output have been developed to measure the output voltage of micropotentiometers (mupots). Using a twin-stage design with gains of 10, 20, and 30 per stage, total gain factors ranging from 10 to 900 are achieved. This results in a usable range of input voltages from 100 muV up to 100 mV at frequencies ranging from dc to 1 MHz. A novel offset compensation results in small reversal differences, and this allows for reliable operation at higher gain factors. There is a sophisticated protection circuit to avoid damage of the PMJTC in the case of overload. The ac-dc transfer difference is flat within 100 muV/V up to 100 kHz.

Systematic Error Analysis of Stepwise-Approximated AC Waveforms Generated by Programmable Josephson Voltage Standards

We have measured stepwise-approximated sine waves generated by a programmable Josephson voltage standard (PJVS) with several different output configurations. These data are analyzed to characterize the dominant error mechanisms for RMS applications, such as AC-DC difference measurements of thermal voltage converters (TVCs). We present detailed explanations of the fundamental causes and consequences of systematic errors that arise from transitions and consider the overall uncertainties for PJVS ac metrology using this synthesis method. We show that timing-related errors are sufficient to make this waveform synthesis approach impractical for RMS audio-frequency applications. The implications of providing the load current required by devices of low input impedance, such as TVCs, are also discussed.

Systematic-Error Signals in the AC Josephson Voltage Standard: Measurement and Reduction

We investigate the dominant frequency-dependent systematic-error signals (SESs) in the AC Josephson voltage standard. We describe our error measurement technique and a number of methods to reduce the errors. Most importantly, we found that a small change in on-chip wiring significantly reduces the SES, improves SES measurement stability, and enables a suitable bias correction method. We show that direct analog-to-digital converter measurements of the SES of two on-chip Josephson arrays are in very good agreement with errors inferred from AC-DC transfer standard measurements. Finally, we demonstrate that the reduction of the SES using these techniques greatly improves the agreement between the AC-DC differences of the two arrays as well as the absolute AC voltage accuracy.

AC–DC Transfer Standard Measurements and Generalized Compensation With the AC Josephson Voltage Standard

We present AC-DC transfer standard measurements using the National Institute of Standards and Technology's pulse-driven AC Josephson voltage standard source. We have investigated the frequency dependence for several output voltages up to 200 mV for frequencies from 2.5 to 100 kHz. We found that, as the frequency increases, the ac-dc differences for the two arrays on the same chip do not agree. We explored this deviation in ac-dc difference for the two arrays by investigating different configurations of the probe cabling and wiring, chip carriers, and on-chip circuit design. We found that the circuit design produced the greatest improvement, particularly at the highest frequency (100 kHz), where the deviation in ac-dc difference was reduced by more than 60%. In this paper, we also demonstrate tenfold higher output voltages and improved operating margins for arbitrary (nonsinusoidal) waveforms. These enhancements were accomplished by implementing a more general current bias to the arrays having the same harmonic content as that of the synthesized arbitrary waveform.

Explanation for the AC–DC Voltage Transfer Differences in Thin-Film Multijunction Thermal Converters on Silicon Chips at High Frequencies

In this paper, an explanation for the ac-dc voltage transfer differences at frequencies greater than 100 kHz of the standard thin-film or planar multijunction thermal converter (PMJTC) developed at the Physikalisch-Technische Bundesanstalt and fabricated on a silicon chip has been found. The simulation indicates that the capacitance of the bond pads of the heater is the reason for an increase of the ac-dc voltage transfer difference of PMJTCs with higher heater resistance to negative values. Bond pads of smaller size and larger distance are shown to improve the frequency response

Quartz Thin-Film Multijunction Thermal Converters With Built-In Tee Connector for 100 MHz

Planar multijunction thermal converters (PMJTC) on quartz crystal chips and membranes have been fabricated. Compared to previous single-junction thermal converters, these devices exhibit calculable and smaller ac-dc voltage transfer differences in the frequency range from 1 MHz to 100 MHz along with a 3- to 10-fold reduction in uncertainty. Built-in Tee connectors are used to avoid the contribution of leads and connectors to the ac-dc voltage transfer difference of the PMJTC chip. The contribution of different designs of built-in Tees to the overall uncertainty of the calculable standard has been evaluated. The uncertainty budgets are discussed in detail

Improvements in the NIST Calibration Service for Thermal Transfer Standards

We report on multiple improvements made in the calibration services offered for thermal converters and thermal transfer standards in the ac-dc Difference Standards and Measurement Techniques Project at NIST during the past year. The major improvement in this calibration is the increased efficiency made possible by the consolidation of three disparate calibration services - low voltage thermal transfer standards, low- frequency thermal converters, and RF-dc difference calibrations - into a single service. This consolidation has the immediate benefit of offering NIST calibration customers one source for ac-dc calibrations from 2 mV to 1000 V and from 10 Hz to 1 GHz. Additional benefits include lower calibration prices and reduced uncertainties at many points.

1-A and-120 mA Thin-Film Multijunction Thermal Converters

We report on the development of thin-film multijunction thermal converters for the measurement of AC currents up to 10 A without relying on parallel current shunts. The materials and designs chosen for these devices have been optimized to provide high accuracy over a wide range of input levels and frequencies. Preliminary measurements on a 10-A chip made with a copper-gold heater indicate that its ac-dc difference is nearly zero from 10 Hz to 100 kHz, and that the AC-DC difference is independent of input current level.